Wafers with etchable sacrificial patterns, anchors, tethers, and printable devices

ABSTRACT

Methods of forming integrated circuit devices include forming a sacrificial layer on a handling substrate and forming a semiconductor active layer on the sacrificial layer. The semiconductor active layer and the sacrificial layer may be selectively etched in sequence to define an semiconductor-on-insulator (SOI) substrate, which includes a first portion of the semiconductor active layer. A multi-layer electrical interconnect network may be formed on the SOI substrate. This multi-layer electrical interconnect network may be encapsulated by an inorganic capping layer that contacts an upper surface of the first portion of the semiconductor active layer. The capping layer and the first portion of the semiconductor active layer may be selectively etched to thereby expose the sacrificial layer. The sacrificial layer may be selectively removed from between the first portion of the semiconductor active layer and the handling substrate to thereby define a suspended integrated circuit chip encapsulated by the capping layer.

REFERENCE TO PRIORITY APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/192,751, filed on Nov. 15, 2018, now U.S. Pat. No. 10,522,575, whichis a continuation of U.S. patent application Ser. No. 15/864,813, filedon Jan. 8, 2018, now U.S. Pat. No. 10,163,945, which is a continuationof U.S. patent application Ser. No. 15/243,228, filed on Aug. 22, 2016,now U.S. Pat. No. 9,899,432, which is a continuation of U.S. patentapplication Ser. No. 14/708,893, filed on May 11, 2015, now U.S. Pat.No. 9,443,883, which is a continuation of U.S. patent application Ser.No. 14/334,179, filed on Jul. 14, 2014, now U.S. Pat. No. 9,040,425,which is a continuation of U.S. patent application Ser. No. 12/732,868,filed on Mar. 26, 2010, now U.S. Pat. No. 8,877,648, which claimspriority from U.S. Provisional Application No. 61/163,535, filed on Mar.26, 2009, the disclosures of which are hereby incorporated by referenceherein in their entireties.

FIELD OF THE INVENTION

The present invention relates to integrated circuit fabrication methodsand, more particularly, to methods of forming integrated circuitsubstrates using semiconductor-on-insulator (SOI) fabricationtechniques.

BACKGROUND OF THE INVENTION

A variety of conventional methods are available for printing integratedcircuit device structures on substrates. Many of these device structuresmay include nano structures, microstructures, flexible electronics,and/or a variety of other patterned structures. Some of these devicestructures are disclosed in U.S. Pat. Nos. 7,195,733 and 7,521,292 andin U.S. Patent Publication Nos. 2007/0032089, 20080108171 and2009/0199960, the disclosures of which are hereby incorporated herein byreference.

Progress has also been made in extending the electronic performancecapabilities of integrated circuit devices on plastic substrates inorder to expand their applicability to a wider range of electronicapplications. For example, several new thin film transistor (TFT)designs have emerged that are compatible with processing on plasticsubstrate materials and may exhibit significantly higher deviceperformance characteristics than thin film transistors having amorphoussilicon, organic, or hybrid organic-inorganic semiconductor elements.For example, U.S. Pat. No. 7,622,367 to Nuzzo et al. and U.S. Pat. No.7,557,367 to Rogers et al. disclose methods of forming a wide range offlexible electronic and optoelectronic devices and arrays of devices onsubstrates containing polymeric materials. The disclosures of U.S. Pat.Nos. 7,557,367 and 7,622,367 are hereby incorporated herein byreference.

SUMMARY OF THE INVENTION

Methods of forming integrated circuit devices according to someembodiments of the invention include forming a sacrificial layer on ahandling substrate and forming a semiconductor active layer on thesacrificial layer. A step is performed to selectively etch through thesemiconductor active layer and the sacrificial layer in sequence todefine a semiconductor-on-insulator (SOI) substrate, which includes afirst portion of the semiconductor active layer. The sacrificial layermay be an electrically insulating layer. A multi-layer electricalinterconnect network may be formed on the SOI substrate. Thismulti-layer electrical interconnect network may be encapsulated by aninorganic capping layer that contacts an upper surface of the firstportion of the semiconductor active layer. This inorganic capping layermay be formed as an amorphous silicon layer or a metal layer, forexample.

The capping layer and the first portion of the semiconductor activelayer can be selectively etched to thereby expose the sacrificial layer.The sacrificial layer may then be selectively removed from between thefirst portion of the semiconductor active layer and the handlingsubstrate to thereby define a suspended integrated circuit chipencapsulated by the capping layer.

According to additional embodiments of the invention, encapsulating theelectrical interconnect network may be preceded by roughening the uppersurface of the first portion of the semiconductor active layer so that agreater level of adhesion can be achieved between the capping layer andthe semiconductor active layer. In some embodiments of the invention,the upper surface may be roughened by exposing the upper surface to aplasma etchant.

According to additional embodiments of the invention, selectivelyetching through the semiconductor active layer and the sacrificial layermay include selectively etching the semiconductor active layer and thesacrificial layer in sequence to define a trench therein having a bottomthat exposes the handling substrate. This trench, which can be aring-shaped trench that surrounds the SOI substrate, can be filled withan inorganic anchor (e.g., semiconductor anchor) in advance of formingthe multi-layer electrical interconnect network. For example, the trenchcan be filled by depositing a semiconductor layer into the trench andonto the SOI substrate and then planarizing the deposited semiconductorlayer to define a semiconductor anchor. In addition, selectivelyremoving the sacrificial insulating layer from between the first portionof the semiconductor active layer and the handling substrate may includeexposing a sidewall of the semiconductor anchor.

In additional embodiments of the invention, the multi-layer electricalinterconnect network includes a plurality of interlayer dielectriclayers, which can be selectively etched to expose the anchor. Theencapsulating step may also include depositing the inorganic cappinglayer directly onto the exposed anchor. In some of these embodiments ofthe invention, the inorganic capping layer is formed as amorphoussilicon and the anchor is formed as polysilicon.

According to additional embodiments of the invention, a method offorming an integrated circuit device may include forming asemiconductor-on-insulator (SOI) substrate anchored at a peripherythereof to an underlying handling substrate. The SOI substrate includesa semiconductor active layer on an underlying sacrificial layer. Themethods further include forming a multi-layer electrical interconnectnetwork, which has a plurality of interlayer dielectric layers, on theSOI substrate. A step is performed to selectively etch through theplurality of interlayer dielectric layers to expose an upper surface ofthe SOI substrate. The multi-layer electrical interconnect network isthen encapsulated with an inorganic capping layer (e.g., a-Si), whichcontacts the exposed upper surface of the SOI substrate. A step isperformed to selectively etch through the capping layer and thesemiconductor active layer to expose the sacrificial layer. Then, thesacrificial layer is removed from the SOI substrate to thereby suspendthe semiconductor active layer from the handling substrate. According tosome of these embodiments of the invention, the step of forming asemiconductor-on-insulator (SOI) substrate may include anchoring the SOIsubstrate to the underlying handling substrate using a ring-shapedpolysilicon anchor. In addition, the step of removing the sacrificiallayer may include removing the sacrificial layer from the SOI substrateto thereby expose a sidewall of the ring-shaped polysilicon anchor.

Methods of forming substrates according to additional embodiments of theinvention include forming a plurality of spaced-apart sacrificialpatterns on a first substrate, such as a glass, quartz, ceramic, plasticmetal or semiconductor substrate, for example. A semiconductor layer isformed on the plurality of spaced-apart sacrificial patterns and onportions of the first substrate extending between sidewalls of theplurality of spaced-apart sacrificial patterns. The semiconductor layeris patterned to define openings therein. These openings exposerespective ones of the plurality of spaced-apart sacrificial patterns. Astep is performed to selectively etch the plurality of spaced-apartsacrificial patterns through the openings to thereby convert at least afirst portion of the patterned semiconductor layer into a plurality ofsuspended semiconductor device layers. These suspended semiconductordevice layers are anchored to a second portion of the patternedsemiconductor layer.

According to additional embodiments of the invention, the step offorming a plurality of spaced-apart sacrificial patterns includesforming a sacrificial layer on the first substrate and then rougheningan upper surface of the sacrificial layer. The roughened surface of thesacrificial layer is then selectively etched to define the plurality ofspaced-apart sacrificial patterns. In these embodiments of theinvention, the step of forming a semiconductor layer includes depositinga semiconductor layer onto the roughened surface of the sacrificiallayer. According to some of these embodiments of the invention, theroughening step may include exposing the surface of the sacrificiallayer to a chemical etchant prior to cleaning. This sacrificial layermay include a material selected from a group consisting of molybdenum,aluminum, copper, nickel, chromium, tungsten, titanium and alloysthereof. In addition, the semiconductor layer may include a materialselected from a group consisting of amorphous silicon, polycrystallinesilicon, nanocrystalline silicon, and indium gallium zinc oxide, forexample.

According to still further embodiments of the invention, the step ofpatterning the semiconductor layer includes selectively etching an uppersurface of the semiconductor layer to define the openings. This step ofselectively etching the upper surface of the semiconductor layer may befollowed by printing the plurality of suspended semiconductor devicelayers onto a second substrate after the plurality of spaced-apartsacrificial patterns have been removed. This printing may be performedby contacting and bonding the upper surface of the semiconductor layerto the second substrate and then fracturing anchors between theplurality of suspended semiconductor device layers and the secondportion of the patterned semiconductor layer by removing the firstsubstrate from the second substrate.

Additional embodiments of the invention include printing substrates byforming a plurality of spaced-apart sacrificial patterns on a firstsubstrate and then forming at least one thin-film transistor on each ofthe plurality of spaced-apart sacrificial patterns. A step is thenperformed to pattern a semiconductor layer associated with each of theplurality of thin-film transistors to define openings therein thatexpose respective ones of the plurality of spaced-apart sacrificialpatterns. The plurality of spaced-apart sacrificial patterns are thenselectively etched through the openings. This selective etching stepconverts at least a first portion of the patterned semiconductor layerinto a plurality of suspended semiconductor device layers, which areanchored to a second portion of the patterned semiconductor layer.Following this step, the plurality of suspended semiconductor devicelayers are printed (e.g., contact bonded) onto a second substrate. Theanchors between the plurality of suspended semiconductor device layersand the second portion of the patterned semiconductor layer are thenfractured by removing the first and second substrates from each other.This fracturing step results in the formation of a plurality ofseparated semiconductor device layers that are bonded to the secondsubstrate.

According to some of these embodiments of the invention, the step offorming at least one thin-film transistor includes forming source anddrain electrodes of a first thin-film transistor on a first sacrificialpattern. An amorphous semiconductor layer is then formed on uppersurfaces of the source and drain electrodes and on sidewalls of thefirst sacrificial pattern. An electrically insulating layer is thenformed on the amorphous semiconductor layer and a gate electrode of thefirst thin-film transistor is formed on the electrically insulatinglayer.

According to alternative embodiments of the invention, the step offorming at least one thin-film transistor includes forming a gateelectrode of a first thin-film transistor on a first sacrificial patternand then forming an electrically insulating layer on the gate electrodeand on sidewalls of the first sacrificial pattern. An amorphoussemiconductor layer is formed on the electrically insulating layer andsource and drain electrodes of the first thin-film transistor are formedon the amorphous semiconductor layer.

Additional embodiments of the invention include forming an array ofsuspended substrates by forming a plurality of spaced-apart sacrificialpatterns on a first substrate. An amorphous semiconductor layer isformed on the plurality of spaced-apart sacrificial patterns and onportions of the first substrate extending between sidewalls of theplurality of spaced-apart sacrificial patterns. Portions of theamorphous semiconductor layer extending opposite the plurality ofspaced-apart sacrificial patterns are then converted into respectivesemiconductor regions having higher degrees of crystallinity thereinrelative to the amorphous semiconductor layer. The amorphoussemiconductor layer is patterned to define openings therein that exposerespective ones of the plurality of spaced-apart sacrificial patterns. Astep is then performed to selectively etch the plurality of spaced-apartsacrificial patterns through the openings to thereby convert at least afirst portion of the patterned amorphous semiconductor layer into aplurality of suspended semiconductor device layers, which are anchoredto a second portion of the patterned amorphous semiconductor layer.According to some embodiments of the invention, the converting stepincludes annealing the portions of the amorphous semiconductor layerextending opposite the plurality of spaced-apart sacrificial patterns.Alternatively, the converting step may include selectively exposing theportions of the amorphous semiconductor layer extending opposite theplurality of spaced-apart sacrificial patterns to laser light.

According to still further embodiments of the invention, the step offorming a plurality of spaced-apart sacrificial patterns includesforming a sacrificial layer on the first substrate and then roughening asurface of the sacrificial layer. A step is then performed toselectively etch the roughened surface of the sacrificial layer todefine the plurality of spaced-apart sacrificial patterns. The step offorming an amorphous semiconductor layer includes depositing anamorphous semiconductor layer on the roughened surface of thesacrificial layer. The roughening step may include exposing the surfaceof the sacrificial layer to a chemical etchant prior to cleaning.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1J are cross-sectional views of intermediate structures thatillustrate methods of forming integrated circuit chips according toembodiments of the present invention.

FIG. 1K is a plan view of an integrated circuit substrate having aplurality of integrated circuit chips therein, according to embodimentsof the present invention.

FIG. 2 is a flow diagram that illustrates fabrication methods accordingto some embodiments of the invention.

FIGS. 3A-3E are cross-sectional views of intermediate structures thatillustrate methods of forming substrates according to embodiments of theinvention.

FIG. 4A is a plan view photograph of an array of suspended substratesaccording to embodiments of the invention.

FIG. 4B is a plan view photograph of an array of substrates that havebeen printed according to embodiments of the invention.

FIG. 5 is a flow diagram that illustrates fabrication methods accordingto some embodiments of the invention.

FIGS. 6A-6C are cross-sectional views of intermediate structures thatillustrate methods of forming substrates according to embodiments of theinvention.

FIGS. 7A-7B are cross-sectional views of intermediate structures thatillustrate methods of forming TFT transistors according to embodimentsof the present invention.

FIGS. 8A-8B are cross-sectional views of intermediate structures thatillustrate methods of forming TFT transistors according to embodimentsof the present invention.

FIGS. 9A-9B are cross-sectional views of intermediate structures thatillustrate methods of forming TFT transistors according to embodimentsof the present invention.

DESCRIPTION OF EMBODIMENTS

The present invention now will be described more fully with reference tothe accompanying drawings, in which preferred embodiments of theinvention are shown. This invention may, however, be embodied in manydifferent forms and should not be construed as being limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likereference numerals refer to like elements throughout.

It will be understood that when an element or layer is referred to asbeing “on,” “connected to” or “coupled to” another element or layer (andvariants thereof), it can be directly on, connected or coupled to theother element or layer or intervening elements or layers may be present.In contrast, when an element is referred to as being “directly on,”“directly connected to” or “directly coupled to” another element orlayer (and variants thereof), there are no intervening elements orlayers present. Like reference numerals refer to like elementsthroughout. As used herein, the term “and/or” includes any and allcombinations of one or more of the associated listed items and may beabbreviated as “/”.

It will be understood that, although the terms first, second, third etc.may be used herein to describe various elements, components, regions,layers and/or sections, these elements, components, regions, layersand/or sections should not be limited by these terms. These terms areonly used to distinguish one element, component, region, layer orsection from another region, layer or section. Thus, a first element,component, region, layer or section discussed below could be termed asecond element, component, region, layer or section without departingfrom the teachings of the present invention.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the term “below” can encompass both an orientation ofabove and below. The device may be otherwise oriented (rotated 90degrees or at other orientations) and the spatially relative descriptorsused herein interpreted accordingly.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the presentinvention. As used herein, the singular forms “a,” “an” and “the” areintended to include the plural forms as well, unless the context clearlyindicates otherwise. It will be further understood that the terms“comprising”, “including”, having” and variants thereof, when used inthis specification, specify the presence of stated features, steps,operations, elements, and/or components, but do not preclude thepresence or addition of one or more other features, steps, operations,elements, components, and/or groups thereof. In contrast, the term“consisting of” when used in this specification, specifies the statedfeatures, steps, operations, elements, and/or components, and precludesadditional features, steps, operations, elements and/or components.

Embodiments of the present invention are described herein with referenceto cross-section and perspective illustrations that are schematicillustrations of idealized embodiments (and intermediate structures) ofthe present invention. As such, variations from the shapes of theillustrations as a result, for example, of manufacturing techniquesand/or tolerances, are to be expected. Thus, embodiments of the presentinvention should not be construed as limited to the particular shapes ofregions illustrated herein but are to include deviations in shapes thatresult, for example, from manufacturing. For example, a sharp angle maybe somewhat rounded due to manufacturing techniques/tolerances.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which the present invention belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

FIG. 1A illustrates forming an integrated circuit device by forming asacrificial layer 12 on a handling substrate 10 (e.g., silicon wafer),forming a semiconductor active layer 14 on the sacrificial layer 12 andforming a field oxide layer 16 on the semiconductor active layer 14.According to some embodiments of the invention, the semiconductor activelayer 14 may be a thinned silicon wafer that is bonded to thesacrificial layer 12 and the sacrificial layer may be an electricallyinsulating layer.

FIGS. 1B-1C illustrate selectively etching through the field oxide layer16, the semiconductor active layer 14 and the sacrificial layer 12 insequence to define trenches 18 therein that expose the handlingsubstrate 10 and define a plurality of semiconductor-on-insulator (SOI)substrates 20 containing respective portions of the semiconductor activelayer 14.

FIG. 1D-1E illustrate filling the trenches 18 with inorganic anchors 24(e.g., semiconductor anchors) by depositing an inorganic layer 22 intothe trenches 18 and onto the SOI substrates 20 and then planarizing thedeposited inorganic layer 22 to define the anchors 24, using the fieldoxide layer 16 as a etch/planarization stop. The inorganic layer 22 maybe a polysilicon layer that is conformally deposited by low-pressurechemical vapor deposition (LPCVD).

FIGS. 1F-1G illustrate forming a plurality of multi-layer electricalinterconnect networks 26 on respective SOI substrates 20, after activedevices (e.g., CMOS devices, not shown) have been formed therein. Eachof these multi-layer electrical interconnect networks 26 may includemultiple layers of metallization and vertical interconnects within astacked composite of multiple interlayer insulating layers 28. As shownby FIG. 1G, an interlayer dielectric layer (ILD) etching step may beperformed to expose the anchors 24, which may be ring-shaped or formedas parallel stripes that extend in a third dimension (see, e.g., FIG.1K), and also expose adjacent portions of the semiconductor active layer14. The exposed portions of the semiconductor active layer 14illustrated by FIG. 1G can then be exposed to a plasma etchant tothereby roughen the exposed upper surfaces of the semiconductor activelayer 14. Plasmas that operate to etch silicon may utilizefluorine-containing gases (e.g., sulfur hexafluoride, SF₆).Alternatively, silicon may be removed from a surface of the active layer14 by exposing the surface to a relatively inert gas containing argonions, for example.

According to alternative embodiments of the invention (not shown), theintermediate structure illustrated by FIG. 1G may be achieved byproviding an SOI substrate having active electronic devices (not shown)within the semiconductor active layer 14 and a plurality of multi-layerelectrical interconnect networks on the active layer 14. The interlayerdielectric layers associated with the multi-layer electricallyinterconnect networks may then be selectively etched to expose theactive layer 14 and then the active layer 14 and the sacrificial layer12 may be selectively etched using a mask (not shown) to define aplurality of trenches having bottoms that expose the handling substrate10. The trenches may then be filled with inorganic anchors prior todeposition of an inorganic capping layer.

Referring now to FIG. 1H, each of the plurality of multi-layerelectrical interconnect networks 26 is encapsulated by depositing aninorganic capping layer 32 that contacts the roughened upper surfaces ofthe semiconductor active layer 14 to thereby form chemically imperviousand etch resistant bonds (e.g., a hermetic seal) at the interfacebetween the capping layer 32 and the roughened surfaces of thesemiconductor active layer 14. The semiconductor capping layer 32 may beformed as an amorphous silicon layer or a metal layer. For example, anamorphous silicon capping layer may be deposited at a temperature ofless than about 350° C. using a plasma-enhanced deposition technique.

FIG. 1I illustrates the formation of through-substrate openings 34 byselectively patterning of the capping layer 32 to define openingstherein followed by the deep etching of the semiconductor active layer14 to thereby expose underlying portions of the sacrificial layer 12 anddefine relatively thin supporting tethers 36 (see, e.g., FIG. 1K).Referring now to FIG. 1J, the sacrificial layer 12 is selectivelyremoved from between the semiconductor active layer 14 and the handlingsubstrate 10 to thereby define a plurality of suspended integratedcircuit chips 40 which are individually encapsulated by the patternedcapping layer 32. During this removal step, which may include exposingthe intermediate structure of FIG. 1I to hydrofluoric acid (HF), thesidewalls of the anchors 24 may be exposed and the capping layer 32 mayoperate to protect the electrical interconnect networks 26 from chemicaletchants. FIG. 1K is a plan view of an integrated circuit substrate ofFIG. 1J (with capping layer 32 removed), which shows thin supportingtethers 36 extending between adjacent portions of the semiconductoractive layer 14. These supporting tethers 36 enable each of theintegrated circuit chips 40 to remain attached to the anchors 24. Thepatterned capping layer 32 may also be removed or remain as apassivating/protective layer.

Referring now to FIG. 2, methods of forming a plurality of functionallayers according to some embodiments of the invention include depositinga sacrificial layer on a substrate (step 1) and then patterning thesacrificial layer (step 2) into a plurality of sacrificial patterns. Afunctional layer is then deposited (step 3) onto the plurality ofsacrificial patterns. The functional layer is then patterned (step 4) todefine openings therein. The sacrificial patterns are then removed (step5) from underneath respective functional patterns. The functionalpatterns are then transferred to another substrate (step 6) by printing,for example.

The methods of FIG. 2 are further illustrated by FIGS. 3A-3E, which arecross-sectional views of intermediate structures. These intermediatestructures illustrate additional methods of forming substrates accordingto embodiments of the invention. FIG. 3A illustrates forming asacrificial layer 52 on a handling substrate 50. The sacrificial layer52 may be formed of an electrically conductive material such asmolybdenum (Mo), aluminum (Al), copper (Cu), nickel (Ni), chromium (Cr),tungsten (W), titanium tungsten (TiW), titanium (Ti) or an electricallyinsulating material such as silicon dioxide, for example. The handlingsubstrate 50 may be a semiconductor wafer, a glass substrate, or aceramic board, for example. In some additional embodiments of theinvention, a step may be performed to increase a roughness of an uppersurface of the sacrificial layer 52 by exposing the upper surface to achemical etchant for a sufficient duration to increase an average RMSroughness of the surface, prior to cleaning.

As illustrated by FIG. 3B, the sacrificial layer 52 is selectivelyetched using a mask (not shown) to define a plurality of spaced-apartsacrificial patterns 52′ and expose portions of the underlying handlingsubstrate 50, as illustrated. Referring now to FIG. 3C, a functionallayer 54 is formed directly on upper surfaces of the plurality ofspaced-apart sacrificial patterns 52′ and directly on the exposedportions of the underlying handling substrate 50. The functional layer54 may be formed as a semiconductor layer, such as a polysilicon layer,an amorphous silicon layer, a nanocrystalline silicon layer, or anindium gallium zinc oxide layer. The amorphous silicon layer may beformed using a plasma enhanced chemical vapor deposition (PECVD)technique. Alternatively, the polysilicon layer, amorphous siliconlayer, nanocrystalline silicon layer or indium gallium zinc oxide layermay be formed using sputtering techniques.

Referring now to FIG. 3D, a patterned functional layer 54 is defined byselectively etching the functional layer 54 of FIG. 3C using a mask (notshown), to define a plurality of openings 56 therein that exposerespective portions of the underlying sacrificial patterns 52′. Asillustrated by FIG. 3E, a selective etching step is performed to removethe sacrificial patterns 52′ from underneath the patterned functionallayer 54 and thereby define a plurality of underlying gaps or recesses55. This selective etching step may include exposing the sacrificialpatterns 52′ to a chemical etchant that passes through the openings inthe functional layer 54 and removes the sacrificial patterns 52′.

As illustrated by FIG. 4A, the removal of the sacrificial patterns 52′may result in the formation of a plurality of suspended semiconductordevice layers 54 that are attached by respective pairs of anchors 58 toa surrounding semiconductor layer. These anchors 58 are formed atdiametrically opposite corners of the device layers 54, which are spacedapart from each other by respective openings 56. Referring now to FIG.4B, the semiconductor device layers 54 may be printed at spaced-apartlocations onto a second substrate 60 using a bonding technique. Thisprinting step may also include fracturing the device layers 54 at therespective anchors 58 by removing the handling substrate 50 from thesecond substrate 60, so that the device layers 54 are provided at spacedlocations on the second substrate 60.

Referring now to FIGS. 5 and 6A-6C, additional embodiments of theinvention include depositing a sacrificial layer onto a first substrate60 (step 1) and then patterning the sacrificial layer to define aplurality of openings therein (step 2) that extend between respectivesacrificial patterns 62. A device layer 64 (e.g., amorphoussemiconductor layer) is then deposited onto the patterned sacrificiallayer and onto portions of the first substrate 60 exposed by theopenings in the sacrificial layer (step 3). Portions of the device layer64 are then treated by thermal and/or laser treatment. For example, inthe event the device layer 64 is an amorphous silicon layer, then theportions of the device layer 64 extending opposite the plurality ofspaced-apart sacrificial patterns 62 may be converted into respectivesemiconductor regions 65 having higher degrees of crystallinity thereinrelative to the surrounding amorphous silicon regions 64′.

The treated device layer 64 is then patterned (step 4) to define aplurality of openings 68 therein between amorphous silicon regions 64′and higher crystallinity regions 65′. These openings 68 exposerespective ones of the plurality of spaced-apart sacrificial patterns62. The sacrificial patterns 62 are then selectively etched through theopenings (step 5) to thereby convert at least a first portion of thepatterned device layer (e.g., amorphous semiconductor layer) into aplurality of suspended semiconductor device layers 65′ that are anchoredto a second portion of the patterned device layer 64′. As illustrated byFIGS. 4A-4B, a transfer printing step (step 6) may be performed totransfer the semiconductor device layers (as functional layers 54) to asecond substrate 60.

FIGS. 7A-7B illustrate methods of forming printable thin-film transistor(TFT) substrates according to additional embodiments of the invention.As illustrated by FIGS. 7A-7B, a sacrificial pattern 75 is formed on afirst substrate 70. A source electrode 76 a and a drain electrode 76 bare formed on the sacrificial pattern 75, as illustrated. Asemiconductor layer 72 (e.g., a-Si) is formed on the source and drainelectrodes, the sacrificial pattern 75 and the substrate 70, asillustrated. Thereafter, an electrically insulating layer 74 is formedon the semiconductor layer 72 and a gate electrode 76 c is formed on theelectrically insulating layer 74. The source, drain and gate electrodes76 a-76 c collectively define the three terminals of a thin-filmtransistor having an active channel region defined within thesemiconductor layer 72. The insulating layer 74 and semiconductor layer72 are then selectively etched to define openings 78 therein. An etchingstep (e.g., wet etching) is then performed to remove the sacrificialpatter 75 from underneath the source and drain electrodes 76 a-76 b andthe semiconductor layer 72, as illustrated. A printing step may then beperformed to print the gate electrode 76 c and insulating layer 74directly onto a second substrate (not shown) prior to removal of thefirst substrate 70. This printing step results in the formation of athin-film transistor (TFT) having exposed source and drain electrodes 76a-76 b.

FIGS. 8A-8B illustrate methods of forming printable thin-film transistor(TFT) substrates according to additional embodiments of the invention.As illustrated by FIG. 8A-8B, a sacrificial pattern 85 is formed on afirst substrate 80. A gate electrode 86 c is formed on the sacrificialpattern 85, as illustrated. An electrically insulating layer 82 is thenformed on the gate electrode 86 c, the sacrificial pattern 85 and thesubstrate 80, as illustrated. Thereafter, a semiconductor layer 84(e.g., a-Si) is formed on the electrically insulating layer 82. Sourceand drain electrodes 86 a-86 b are formed on the semiconductor layer 84.The source, drain and gate electrodes 86 a-86 c collectively define thethree terminals of a thin-film transistor having an active channelregion defined within the semiconductor layer 84. The semiconductorlayer 84 and insulating layer 82 are then selectively etched to defineopenings 88 therein. An etching step (e.g., wet etching) is thenperformed to remove the sacrificial patter 85 from underneath the gateelectrode 86 c and the insulating layer 82, as illustrated. A printingstep may then be performed to print the source and drain electrodes 86a-86 b and semiconductor layer 84 directly onto a second substrate (notshown) prior to removal of the first substrate 80. This printing stepresults in the formation of a thin-film transistor (TFT) having anexposed gate electrode 86 c.

FIGS. 9A-9B illustrate methods of forming printable thin-film transistor(TFT) substrates according to additional embodiments of the invention.As illustrated by FIGS. 9A-9B, a sacrificial pattern 95 is formed on afirst substrate 90. A semiconductor layer 92 (e.g., a-Si) is formed onthe sacrificial pattern 95 and the first substrate 90, as illustrated.Thereafter, an electrically insulating layer 94 having an embedded gateelectrode 96 a therein is formed on the semiconductor layer 92. Sourceand drain electrodes 96 b-96 c are then formed on the insulating layer94. These source and drain electrodes use source and drain electrodeplugs 96 b′ and 96 c′, which extend through the electrically insulatinglayer 94, to contact the semiconductor layer 92, as illustrated. Theinsulating layer 94 and semiconductor layer 92 are then selectivelyetched to define openings 98 therein. An etching step (e.g., wetetching) is then performed to remove the sacrificial patter 95 fromunderneath the semiconductor layer 92, as illustrated. A printing stepmay then be performed to print the source and drain electrodes 96 b-96 cand insulating layer 94 directly onto a second substrate (not shown)prior to removal of the first substrate 90. This printing step resultsin the formation of a thin-film transistor (TFT) having buried sourceand drain electrodes 96 b-96 c.

In the drawings and specification, there have been disclosed typicalpreferred embodiments of the invention and, although specific terms areemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the invention being set forthin the following claims.

That which is claimed:
 1. A wafer of devices, comprising: a substrate,the substrate comprising anchors separated by spaced-apart sacrificialpatterns; devices, each disposed entirely over one of the sacrificialpatterns; and tethers, wherein for each of the tethers, the tetherextends between a device of the devices and an anchor of the anchorsthat is adjacent to the device to attach the device to the anchor,wherein the tether is formed from an encapsulating capping layer thatextends over the device.
 2. The wafer of claim 1, wherein the tetherextends over the anchor.
 3. The wafer of claim 1, wherein the tether isdisposed in a common layer with at least a portion of the device.
 4. Thewafer of claim 1, wherein each of the spaced-apart sacrificial patternscomprises a material that is differentially etchable from the anchors.5. The wafer of claim 1, wherein each of the devices is a semiconductordevice.
 6. The wafer of claim 1, wherein each of the devices comprises amulti-layer interconnect network.
 7. The wafer of claim 1, wherein eachof the anchors has a thickness greater than a thickness of each of thesacrificial patterns.
 8. The wafer of claim 1, wherein each of thesacrificial patterns is exposed.
 9. The wafer of claim 1, wherein thesubstrate is a semiconductor substrate, a silicon substrate, or a glasssubstrate.
 10. The wafer of claim 9, wherein the substrate is a siliconsubstrate or a glass substrate.
 11. The wafer of claim 1, wherein thesubstrate is a glass substrate.
 12. The wafer of claim 1, wherein eachof the devices is an active electronic device.
 13. The wafer of claim 1,wherein each of the devices is an integrated circuit.
 14. The wafer ofclaim 1, wherein each of the devices comprises a silicon-on-insulatorsubstrate.
 15. The wafer of claim 1, wherein each of the sacrificialpatterns is a patterned oxide layer.
 16. The wafer of claim 1, whereinthe anchor and the device are laterally adjacent and the tether extendslaterally between the anchor and the device to attach the device to theanchor.
 17. A wafer of devices, comprising: a substrate, the substratecomprising anchors separated by spaced-apart recesses; and devices, eachdisposed entirely over one of the recesses and connected to one of theanchors that is adjacent to the device by a tether, wherein the tetheris formed from an encapsulating capping layer that extends over thedevice.
 18. The wafer of claim 17, wherein the tether extends laterallyto the one of the anchors to suspend the device over the one of therecesses.